> Realistically speaking if you're doing CPU intensive tasks then Node is definitely the wrong solution

Here's the answer:

Spawn $(nproc) more Node processes, use IPC if you need to.

Good luck seizing the theoretical performance gains one might see from threading (while not falling victim to diminishing returns related to context switching) in another comparable language.

Actually I think that even a lot of CPU intensive tasks could run on Node. Split them into smaller tasks (which you probably have to do anyway if you want to use multiple threads with another language) and run those as promises. Of course js is bad for most numerical calculation but for some things it might work. Or combine it with Dart or Asm.js.

You can also use multiple worker processes for your more intensive cpu tasks, keeping that out of your main loop altogether. Pooling and queue limits can prevent too many of those bound processes from running at once, and you can distribute workers across several systems.